It runs for 20+ minutes on a charge, due to the simplicity of the circuit and just the right battery.

Thanks, back when I designed The Caterpillar, I was still working with All Analog circuits, so I hardwired it with 74hc240 inverters using BEAM principles, that gives it a nice organic behavior; now that I have been working with microcontrollers for awhile I have had the notion to combine analog and digital circuitry.